As an exhaust gas purification catalyst arranged in an exhaust passage of an internal combustion engine, there has been developed an electrically heated catalyst (hereinafter, may also be referred to as an EHC) in which a catalyst is heated by means of a heat generation element which generates heat by electrical energization thereof.
Here, there is known a technology in which in a hybrid vehicle, electric resistance is detected at the time of electrical energization of an electrically heated catalyst, so that an abnormality in the electrically heated catalyst is determined based on the electric resistance thus detected (for example, refer to a first patent literature).
In addition, there is also known a technology of estimating the temperature of a mat which serves to support a catalyst (for example, refer to a second patent literature).
Moreover, there is also known a technology in which leakage of electricity or short circuit is determined based on an electric current, a voltage or the like at the time when a high voltage is applied to discharge electrodes, and when a short circuit occurs, the supply of electric power is limited (for example, refer to a third patent literature).
However, when an internal combustion engine is started in a state where the temperature of an electrically heated catalyst is not high enough, water or moisture may condense in an electrically heated catalyst. A value of an insulation resistance between the electrically heated catalyst and an exhaust passage is changed due to this condensed water. In the past, a change in the value of the insulation resistance due to the condensed water is not taken into consideration, so there is a fear that accuracy in detecting an abnormality may become low.